1. Technical Field
The present invention relates to a power train control device, and more particularly relates to a power train control device for a part-time all-wheel drive (AWD) vehicle equipped with an automatic transmission which has an automatic neutral function.
2. Related Art
Conventionally, there has been known technology so called automatic neutral control in which, when the shift position of a vehicle is in the drive (D) range (drive position) but the throttle is generally full-open and the vehicle is stopped due to the brake pedal being applied, for example, the automatic transmission is placed in a neutral state to improve fuel consumption (see Japanese Unexamined Patent Application Publication No. 2005-83492). This automatic neutral control is realized by a half-engaged state (half clutch state) of a driving clutch (clutch for automatic neutral control).
Also, there have conventionally been known two types of AWD: one is full-time AWD, and the other is part-time AWD which can switch between two-wheel drive and four-wheel drive as necessary. Full-time AWD realizes four-wheel drive by providing a center differential between the front wheels and rear wheels, so as to permit differential driving of the front and rear wheels. On the other hand, part time AWD vehicles have, for example, main drive wheels directly linked to the engine, and driven wheels (sub-drive wheels) connected to the engine via a transfer clutch. This configuration allows switching between two-wheel drive and A our-wheel drive through adjustment of distribution of driving force to the driven wheels, by controlling the engaging force of the transfer clutch according to road conditions, driving state, and so forth.
In the case where automatic neutral control is applied to a part-time AWD vehicle having an automatic transmission, juddering may occur at the time of returning from automatic neutral control, i.e., when the driving clutch (clutch for automatic neutral control) is engaged. There has been demand for reduction of this juddering.
Upon diligent study of the aforementioned problem, the present inventor has found that at the time of returning from automatic neutral control in part-time AWD vehicles, vibrations at the time of engaging the driving clutch (clutch for automatic neutral control) are propagated to the driving system of the driven wheels as well, and these vibrations shake the entire power train (the entire vehicle), resulting in juddering when returning from automatic neutral control.